The present invention generally pertains to distance measurement techniques and is particularly directed to determining the position of a ship in relation to predetermined positions on the ocean floor. The present invention is especially useful for precisely determining the position of a survey vessel or an ocean mining ship.
Throughout the exploration phase of ocean mining it has become clear that precise determination of the positions of survey vessels and mining ships is essential to successful economic exploitation of known nodule deposits. Navigation techniques used to date have provided limited positional accuracy over limited operating areas. However, such is generally understood to be insufficient to ensure operational efficiency of developed mining systems.
Precise determination of ship's position over large operational areas in relation to predetermined positions on the ocean floor enhances the ability to dredge more desirable locations on the ocean floor and to avoid, with greater certainty, hazardous areas which may contain rock outcrops, boulders and other obstructions. Also it decreases the chances of dredging the same floor positions more than once or of leaving large areas undredged. It further decreases the chances of inadvertent claim jumping.
Operational efficiency depends on precise determination of the ship's position over large operating areas, which also directly impacts the economics of the entire mining operation. A total solution requires an independent navigation system which is easily established, reliably operated for years in an unattended mode and simply relocated as necessary, and demands a minimum of operational schedule disruption and personnel training for the operator.
The precision navigation system must provide accurate, repeatable, virtually continuous position location data to support deep sea mining operations. The mining ship operation typically will take place in the open-ocean, hundreds of miles from the nearest land and in water depth of about 15,000 feet.
Electronic distance measurement techniques have been utilized to determine the position of a ship. A transceiver on the ship sends ranging interrogation signals to transponders located at predetermined positions and receives ranging response signals in response thereto. The range of the ship from each transponder is determined by processing the received ranging response signals in relation to the ranging interrogation signals, and the position of the ship in relation to the predetermined positions of the transponders is determined by multilateralization. However, ocean mining operations typically are too far from land to enable determination of the ship's position by multilateralization processing utilizing land based electronic distance measuring equipment.
Few conventional navigational aids are available in ocean mining areas. They are the Navigational Satellite System, the Omega navigation system, and inertial reference systems. None of these systems can meet the required positional accuracy for deep ocean mining surveys and/or operations.
For example, the satellite system provides positional accuracy of only about one-quarter nautical mile and the Omega system is accurate to only about 1 mile.